The present invention relates to vehicle wheel service systems, and in particular, to a method of operation for vehicle wheel service systems such as wheel balancers and tire changers configured to illuminate a surface of a wheel rim and tire assembly with a light source or laser, such as to project a display of information onto a surface of vehicle wheel rim or, to optically acquire one or more measurements from a feature on the illuminated surface, to facilitate completion of a wheel imbalance measurement or correction procedure.
When performing vehicle wheel service procedures, such as the mounting of a tire onto a vehicle wheel rim, or the balancing of a wheel rim and tire assembly, it is known to utilize non-contact methods to acquire measurements associated with the vehicle wheel rim and tire assembly, or to display information to an operator directly on a surface of the vehicle wheel rim and tire assembly. Optically-based non-contact methods commonly utilize a laser or other visible light source to project a visible feature onto a surface of the vehicle wheel rim and tire assembly, which is either observed by an operator or imaged by an optical sensor to assist in the completion of a vehicle wheel service procedure
For example, in a vehicle wheel balancer application, during the balancing a vehicle wheel rim and tire assembly, several potential sources for operator error exist which can be alleviated with the use of visible features projected onto the surface of a wheel rim and tire assembly. First, there is a need to identify the proper correction planes on the wheel rim at which imbalance correction weights are to be placed. Second, the wheel rim and tire assembly must be correctly rotated to, and held in, a rotational position such that the operator can place an imbalance correction weight in the identified correction plane, and third, the operator must manually apply the imbalance correction weight to the wheel rim in the identified correction plane and at the proper rotational position.
The determination of unbalance in vehicle wheel rim and tire assemblies is generally carried out by an analysis of the phase and amplitude of the mechanical vibrations caused by the rotating unbalanced mass of the wheel rim and tire assembly. The mechanical vibrations are measured as motions, forces, or pressures by means of transducers, which convert the mechanical vibrations to electrical signals. The electrical signals are subsequently analyzed by a suitably programmed microprocessor. Each electrical signal is representative of a combination of fundamental oscillations caused by the rotating imbalance mass and noise.
It is well known in the art that a variety of types of imbalance correction weights are available for placing on a wheel rim to correct a measured imbalance. For example, adhesive-backed weights, patch balance weights, and hammer-on weights are available from a number of different manufacturers. Most wheel balancer systems are configured to assume that the wheel rim and tire assembly will be rotated to a particular rotational position (for example, disposing the desired weight correction position at the top—twelve o'clock—or bottom—six o'clock—rotational positions) during placement of an imbalance correction weight. This is generally not a problem, unless it is more convenient to apply the weight with the wheel rim and tire assembly in a different rotational position, for example, the four or five o'clock rotational positions, when the operator is standing facing the surface of the wheel rim and tire assembly mounted on the wheel balancer system.
To compensate for a combination of static imbalance (where the heaviest part of the wheel rim and tire assembly will naturally tend towards a rotational position directly below the mounting shaft) and couple imbalance (where the rotating wheel rim and tire assembly exerts torsional vibrations on the mounting shaft), at least two correction weights are typically required to be separated axially along the wheel rim surface, coincident with weight location or imbalance correction “planes”. For imbalance correction weights of the “clip-on” style, the “left plane” comprises the left (innermost) rim lip circumference while the “right plane” comprises the right rim lip. If imbalance correction weights of the “adhesive” style are used, the imbalance correction planes can reside anywhere between the rim lips, barring physical obstruction such as wheel spokes, valve stems, welds, or regions of excessive wheel rim curvature.
During a wheel balancing procedure, the wheel rim and tire assembly is initially mounted to the wheel balancer system, and a scan of the wheel rim inner surface profiles is optionally acquired, either with a mechanical contact system, such as is described in U.S. Pat. No. 6,484,574 B1 to Douglas et. al. or a non-contact measurement system, such as is described in U.S. Pat. No. 6,535,281 B2 to Conheady, et al.
Next, the imbalance correction planes are selected and the relative distances from a reference plane (usually the surface of the wheel mounting hub) to each of the imbalance correction planes is measured either by manual measurement with a pull-out gauge and the observed values provided to the microprocessor, or by using an automatic electronic measuring apparatus to electronically provide a direct measurement of the relative distance to the wheel balancer microprocessor. The radius of the wheel rim at which the weights will be placed must also be provided to the microprocessor, either manually, or by use of the electronic measuring apparatus.
The microprocessors employed by conventional vehicle wheel balancers are generally configured to utilize the input weight plane information, together with variable weight amounts and variable radial placements, to identify proper locations for placement of the imbalance correction weights on the wheel rim, and optionally, to control rotation of the wheel rim and tire assembly. While utilization of such a balancer system facilitates the placement of an imbalance correction weight by placing the vehicle wheel rim and tire assembly in a preferred, or optimal rotational position for placement of the imbalance correction weight, it does not reduce other sources of operator error, such as the placement of an imbalance weight in the incorrect balance plane, a poor selection of imbalance planes by the operator, or failure to compensate for the width of the installed imbalance weights.
Automatic positioning of the wheel rim and tire assembly to a predetermined imbalance correction weight placement rotational position can be enhanced with the addition of a visual guide to the operator. In a basic embodiment, the vehicle wheel balancer system is provided with a laser projection system under control of the microprocessor for projecting a laser dot or illuminated point of light onto a surface of the vehicle wheel rim and tire assembly at a location corresponding to an imbalance correction plane. The laser dot or point of light may be continuously projected onto the wheel rim and tire surface, or illuminated only when the wheel is rotated such that an imbalance correction weight rotational position is aligned with a predetermined rotational about the axis of the balance shaft, such as shown in U.S. Pat. No. 6,244,108 B1 to McInnes et al.
An improvement over selective illumination of the wheel rim and tire assembly surfaces is seen in U.S. Pat. No. 6,484,574 B1 to Douglas et al., which combines a continuous laser projection guide with a wheel balancer system including a direct current motor. A control circuit controls the application of direct current to the direct current motor and determines from vibrations measured by a vibration sensor assembly, at least one weight placement position on the wheel rim and tire assembly to correct the vibrations. The control circuit is responsive to determination of an imbalance correction weight plane to project a laser projection onto the surface of the wheel rim at the selected imbalance correction plane. The controller then rotates the wheel rim and tire assembly to bring the weight placement position to a predetermined rotational location coinciding with the laser projection in the imbalance correction weight plane, and to actively hold the wheel rim and tire assembly in that rotational location at which an imbalance correction weight is to be placed.
In addition to providing guidance to an operator during placement of an imbalance correction weight, the illuminated surface of the vehicle wheel rim and tire assembly may optionally be observed or imaged by a sensor operatively coupled to the vehicle wheel balancer microprocessor. Images of the illumined surface, including the laser dot or point, may be utilized to acquire one or more measurements associated with the vehicle wheel rim and tire assembly, such as shown in U.S. Pat. No. 6,535,281 B2 to Conheady et al.
Regardless of the manner of operation of a vehicle wheel service system configured to illuminate a surface of a vehicle wheel rim and tire assembly, the wide variation in the optical characteristics of vehicle wheel rim and tire assembly surfaces can render such systems non-functional. In particular, vehicle wheel rim and tire assemblies in which the vehicle wheel rim surface is finished in a highly reflective polish or coating, such as chrome, can result in highly limited angles of reflection, unpredictable reflections, or distortions in the illuminating light or laser rendering it difficult or impossible for the operator or an imaging sensor to identify an intended illuminated point, dot, image, or feature on the wheel rim surface.
Accordingly, it would be advantageous to provide a method of operation for vehicle wheel service systems configured to illuminate a surface of a vehicle wheel rim and tire assembly, either for purposes of operator guidance or to acquire one or more measurements of a vehicle wheel rim and tire characteristic, which alters the optical characteristics of the vehicle wheel rim and tire assembly surfaces to enable the surfaces to be illuminated and observed in a desired manner.